Milk feeds were given through indwelling nasogastric tubes to 14 infants with respiratory distress. Similar cardiorespiratory disturbances were observed when the infants were fed (5 ml/kg per feed) human milk, cow's mild, or distilled water. Pao2 fell after a feed but recovered to the prefeed value at 30 minutes, at which time Paco2 had fallen and the respiratory rate had increased. No changes in pH, heart rate, or blood pressure were observed. Portal sinus pressures rose after feeding in association with an increase in central venous pressure. In contrast, when the ill infants were fed human milk at a volume of 2-5 ml/kg per feed no consistent changes in any of the measurements were found. These studies suggested that the cardiorespiratory effects were related to volume displacement resulting from feeds being introduced into the stomach. The relation of the increase in central venous pressure and the magnitude and direction of shunting in infants with the respiratory distress syndrome is uncertain. Adverse effects may be avoided by giving smaller, and therefore even more frequent, feeds.